Central venous catheter having a soft tip and fiber optics

ABSTRACT

A multiple lumen catheter having a soft, tapered multiple lumen distal tip for insertion into a body vessel. One of the lumens is sized to pass over a guidewire such that the catheter can be inserted into the body vessel using the Seldinger technique. At least one medical implement lumen is used for placement or positioning of a biomedical sensor or other medical implement. For example, at least one optical fiber passing through the medical implement lumen may transmit and receive light at the distal tip for measuring oxygen saturation of the blood. The catheter may have a cylindrical catheter body to which the soft distal tip attaches. The soft tip reduces the possibility of vessel or tissue puncture and abrasion. The tip is constructed of a soft plastic or pliable material that yields easily when force is applied. For example, the tip may be made of a softer material than the catheter body, or if made of the same material, the tip can be configured with thinner walls or a higher air-to-material ratio cross-section. Various geometrical configurations and combinations of materials can be used to decrease the resistance of the tip to an applied load. One particular useful application for the catheter of the present invention is as a central venous catheter equipped with fibers for measuring oximetry. The fibers extend to the distal end of the tip and are preferably secured therein with minimal adhesive so as to limit the stiffness added to the tip. One particular useful construction is to secure the fibers within the medical implement lumen using adhesive only along a length of between about 0.5–3.5 mm.

BACKGROUND OF THE INVENTION

The present invention relates generally to medical devices and, moreparticularly, to a central venous catheter having a multilumen soft tipwhose flexibility is not compromised when a medical implement is locatedin one of the lumens of the soft tip during the use of the catheter.Even more specifically, the above-mentioned medical implement is fiberoptics for measuring oxygen saturation of blood.

Central venous (CV) catheters are used primarily to gain access to thevenous vasculature for fluid infusion, blood sampling and central venouspressure monitoring. CV catheters are inserted into the patient usingthe Seldinger technique. This involves identifying the target vein,puncturing the vein and inserting a guidewire. A vessel dilator isinserted over the guidewire and pushed through the vessel wall to createan opening for the CV catheter. The dilator is removed though theguidewire remains in place. The single lumen CV catheter is thenthreaded over the guidewire and pushed through the tissue and into thevessel. Importantly, the catheter is inserted without any stiffeningmembers other than the guidewire. The tissue and vessel wall resist thecatheter as it slides into the vessel. Therefore, to insure the cathetercan easily slide into the body, the catheter body and catheter tip mustbe sufficiently rigid to slide over the guidewire into the blood vesselwithout buckling or otherwise collapsing. More than one lumen in thedistal tip creates an asymmetry in the transverse cross-section andincreases the chances of buckling. Therefore, CV catheters are uniformlyconstructed with a single lumen at the distal tip. Of course, anycatheters that require such a soft tip are at present single lumen, notjust CV catheters.

Once a CV catheter is placed into the blood vessel, then the stiffnessthat was desirable during insertion through the vessel wall becomes adisadvantage. Vessel perforation is always a concern in the design ofthese catheters. Another concern is that the catheter tip migrates fromthe central vena cava to the right atrium. The right atrium containsregions of thick and thin walls. During routine monitoring, if catheterhas migrated into the right atrium, through the action of normal heartbeats, and lodges into the heart wall in one of the thin walls sections,the catheter tip can punch through the atrial wall and create cardiactamponade. If the superior vena cava above the pericardial sac isperforated, a pleural infusion is created, leaking fluid into thepleural or lung cavity. During use, a stiff catheter and tip increasesthe possibility of endothelial abrasion and vessel wall or right atriumwall perforation. Such perforation generally requires surgicalintervention to resolve.

Because of these dangers, CV catheters typically include a soft distaltip that yields when it contacts a vessel wall, and a radiopaque markeris incorporated into the tip to monitor its location within the body.This reduces, but does not eliminate, the possibility of the catheterperforating the vessel wall during repeated contact during use.Therefore, CV catheters tips have been made with softer materials toyield more easily when contacting a vessel wall. Such tips are made ofmaterials such as low durometer urethanes, for example Tecoflex andPellethane, due to their high durability and ease of manufacturing.Importantly, however, all commercially available CV catheters with softdistal tips have one common feature—their distal tip has only a singlelumen which is used for passing a guidewire during insertion and laterduring the use of the catheter may serve for fluid infusion. Such alumen extending through the distal tip does not have any medicalimplement, for example, a sensor or a probe, located within because itwould compromise the flexibility of the soft tip and would alsointerfere with the passing of the guidewire during insertion.

Pulmonary artery (PA) catheters, on the other hand, have blunt rigidtips because they are inserted through a vascular access introducer.Such an introducer has already been positioned within the target vessel,and includes a large bore port through which the PA catheter can bepassed, and a hemostasis valve on its proximal end to prevent bloodleakage around the catheter. Furthermore, many PA catheters require astiff blunt tip to interface more efficiently with an in vitrocalibrating device. Moreover, such stiff, flat tips are relatively easyto manufacture and facilitate polishing of the distal end of the opticalfibers. Therefore, typically there is no need for a soft, tapered distalend on PA catheters. Consequently, rigid tipped catheters may includemultiple lumens in their distal tips.

Mixed venous oxygen saturation (SvO₂) is the amount of oxygen in bloodtaken from a vessel coming from the right side of the heart going intothe lungs. This reflects the amount of oxygen being delivered to thetissues during cardiac arrest and shock. Selective venous hypoxemia orlow oxygen content, when compared to arterial blood, ischaracteristically seen during cardiac arrest and shock.

When oxygen delivery to the tissues is low, the SvO₂ is low. When oxygendelivery to the tissues is high, the SvO₂ is normal or high. Thisprovides the physiological basis for using SvO₂ as an indicator ofresponse to therapy while treating a patient in cardiac arrest or shock.Intermittent SvO₂ measurement can be predictive of outcome in cardiacpatients and hemodynamically unstable trauma patients and medicalpatients.

Typically, SvO₂ is drawn from a pulmonary artery (PA) catheter which isbetween 65–110 centimeters long and is placed into a vein that accessesthe right side of the heart and then into the pulmonary artery. However,placement of a PA catheter is extremely difficult and can be impracticalduring cardiac arrest and severe shock due to low blood pressure.

The central venous system is located much closer to the skin and can bemore easily accessed during shock and cardiac arrest. Thus, a number ofstudies have supported the substitution of central venous (right atrialor superior vena cava) oxygen saturation (ScvO₂) for pulmonary arteryblood oxygen saturation (SvO₂) during spontaneous circulation,circulatory failure, and closed chest CPR. The central venous blood canbe obtained much more easily than blood from the pulmonary artery underconditions of shock and cardiac arrest. Thus, it is more feasible to usethe central venous system as it provides similar information.

Fiber optic technology has previously been utilized in measuring ScvO₂.U.S. Pat. No. 5,315,995 to Rivers ('995), issued May 31, 1994, describesa fiber optic catheter and its efficacy for continuous measurement ofcentral venous oxygen saturation. The catheter includes a catheter bodyhaving a fiber optic bundle disposed therein. In operation, thiscatheter is inserted into the subclavian vein or internal jugular veinwith the aid of a catheter introducer or guide wire. The '995 patent,however, does not teach a soft multiple lumen tip at all and does noteven address the issue of keeping the distal tip of the catheter softand flexible during use despite the presence of a fiber optic bundle.

Currently, there is no answer to the problem of keeping a CV cathetertip flexible when multiple lumens are required at the distal tip, letalone when one or more of the lumens contains a medical implement.Accordingly, there is a need for an improved central venous catheterhaving a soft tip that has multiple lumens and can measure physiologicparameters without the need for multiple catheter insertions.

SUMMARY OF THE INVENTION

The present invention provides a multiple lumen central venous catheterhaving a soft tip. The catheter includes a generally tubular catheterbody having a proximal end and a distal end, the catheter body definingtherein at least one primary lumen and at least one medical implementlumen. A soft, tapered distal catheter tip has a distal end and aproximal end abutting the distal end of the catheter body. The cathetertip defines at least one primary lumen aligned with the at least oneprimary lumen of the catheter body and at least one medical implementlumen aligned with the at least one medical implement lumen of thecatheter body. At least one optical fiber extends through the cathetermedical implement lumens of the catheter body and the catheter tip, andis secured thereto only at the distal end of the catheter tip.

Desirably, the at least one optical fiber extends to a distal face ofthe catheter tip and be secured thereto. The optical fiber may besecured using adhesive that is only applied along a short portion of themedical implement lumen having an axial length of between 0.5–3.5 mm.The adhesive may be cured by ultraviolet light, wherein a portion of thecatheter tip permits passage of ultraviolet light therethrough into themedical implement lumen. Further, the catheter tip may be formed of twomaterials. For example, one material may comprise the portion thatpermits passage of ultraviolet light, and another material that providesa radiopaque marker.

In one embodiment, the catheter tip has at least two exterior taperangles (one in a proximal region and one in a distal region of thecatheter tip), and the proximal region may have a greater taper anglethan the distal region. Desirably, at least one of the proximal anddistal regions of the catheter tip is more flexible than the catheterbody and forms a bending portion of the catheter tip. At least one ofthe proximal and distal regions may be made of a material that has adurometer of less than or equal to 100 Shore A hardness. The proximalregion may have a larger air-to-material ratio in transversecross-section than the distal region Preferably, in transversecross-section, both the at least one primary lumen and the at least onemedical implement lumen are enlarged in the proximal region relative tothe surrounding material in comparison to the relative size of thelumens and material in the distal region, such that the proximal regionhas a larger air-to-material ratio than the distal region.

The catheter tip of the central venous catheter desirably has a lengthof at least 7.6 mm (0.30 inches).

Another aspect of the invention is a multiple lumen central venouscatheter having a soft tip, including a generally tubular catheter bodyhaving a proximal end and a distal end, the catheter body definingtherein at least one primary lumen and at least one medical implementlumen. A soft, tapered distal catheter tip has a proximal end that abutsthe distal end of the catheter body and a distal end. The catheter tipdefines at least one primary lumen aligned with the at least one primarylumen of the catheter body and at least one medical implement lumenaligned with the at least one medical implement lumen of the catheterbody. The catheter tip comprises a proximal region and a distal regionwherein at least one of the proximal and distal regions is more flexiblethan the catheter body.

In one exemplary embodiment, the proximal and distal regions arecomprised of different materials. In another embodiment, a medicalimplement is extending through the medical implement lumens of thecatheter body and the catheter tip and could be secured at the distalend of the catheter tip.

A still further aspect of the invention is a central venous catheterhaving a soft tip, comprising a generally tubular catheter body and asoft, tapered distal catheter tip. The catheter body has a proximal endand a distal end, and defines therein at least one primary lumen and atleast one medical implement lumen. The catheter tip includes a proximalend abutting the distal end of the catheter body and a distal end, andfurther defines within at least one primary lumen aligned with the atleast one primary lumen of the catheter body and at least one medicalimplement lumen aligned with the at least one medical implement lumen ofthe catheter body. The catheter tip has sufficient column strength toresist buckling during insertion using the Seldinger technique over aguidewire, but is sufficiently flexible to deform when the tip issubjected to axial or radial loads in the body in the absence of theguidewire. The catheter further incorporates a sensor extending throughthe medical implement lumen of the catheter body and the medicalimplement lumen of the catheter tip.

In one embodiment, the sensor extends to a distal face of the cathetertip and is secured thereto using adhesive. The sensor may be securedusing adhesive that is only applied along a short portion of the medicalimplement lumen having an axial length of between 0.5–3.5 mm. Theadhesive may be cured by ultraviolet light, wherein a portion of thecatheter tip permits passage of ultraviolet light therethrough into themedical implement lumen. Further, the catheter tip may be formed of twomaterials.

The sensor is selected from the exemplary group consisting of one ormore optical fibers, a pH sensor, a pressure sensor, a temperaturesensor, at least one pacing lead, and a pacing electrode. The sensorcould be a probe that is removable from the catheter.

In another embodiment, the catheter tip has at least two exterior taperangles, and the proximal region has a greater taper angle than thedistal region. Desirably, at least one of the proximal and distalregions is more flexible than the catheter body and forms a bendingportion of the catheter tip. At least one of the proximal and distalregions may be made of a material that has a durometer of less than orequal to 100 Shore A hardness. The proximal region may have a largerair-to-material ratio in transverse cross-section than the distalregion.

The present invention also teaches a method of measuring oxygensaturation of the venous system, comprising the steps of:

-   -   providing a central venous catheter having a catheter body and a        soft, multiple lumen catheter tip, the catheter tip tapering        down from a proximal end to a distal end;    -   providing at least one optical fiber extending through the        catheter body to the distal end of the catheter tip;    -   inserting the central venous catheter into a venous system        vessel using the Seldinger technique;    -   advancing the catheter tip of the central venous catheter into a        location in the venous system for measuring oxygen saturation of        the venous blood; and    -   measuring oxygen saturation of venous blood using the optical        fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are longitudinal sectional and end elevational views,respectively, of a central venous catheter of the prior art having asingle lumen tip;

FIG. 2A is a partial sectional view of a taper-tipped prior art cathetersimilar to that shown in FIG. 1A traveling over a guidewire and justprior to insertion into a body vessel;

FIG. 2B is a graph generally illustrating the reaction force experiencedby the operator when the inserting the catheter of FIG. 2A into thevessel;

FIG. 3A is a partial sectional view of a blunt-tipped prior art cathetertraveling over a guidewire and just prior to insertion into a bodyvessel;

FIG. 3B is a graph generally illustrating the reaction force experiencedby the operator when the inserting the catheter of FIG. 3A into thevessel;

FIG. 4 is a side elevational view of a typical pulmonary artery (PA)catheter of the prior art;

FIGS. 5A and 5B are perspective and longitudinal sectional views,respectively, of a central venous catheter of the prior art thatincludes fiber optics extending through a lumen to the rigid distal tip;

FIGS. 6A and 6B are transverse sectional views through the catheter ofFIGS. 5A and 5B, taken along lines 6A—6A and 6B—6B, respectively;

FIGS. 7A and 7B are longitudinal sectional and end elevational views,respectively, of a central venous catheter of the present inventionhaving a soft multiple lumen tip;

FIG. 7C is a transverse sectional view through the catheter of FIG. 7A,taken along lines 7C—7C and slightly enlarged;

FIG. 8A is a perspective view of a soft multiple lumen distal tip of analternative catheter of the present invention;

FIG. 8B is an exploded, partial sectional view of the catheter distaltip of FIG. 8A and a sensor probe used therewith;

FIGS. 9A and 9B are longitudinal sectional and end elevational views,respectively, of an alternative soft multiple lumen catheter tip of thepresent invention having multiple tapers;

FIG. 9C is a schematic elevational view illustrating material removedfrom the exterior of the catheter tip of FIG. 9A so as to form themultiple tapers and create a bending focal point;

FIGS. 9D and 9E are transverse sectional views through the catheter ofFIG. 9A, taken along lines 9D—9D and 9E—9E, respectively;

FIGS. 10A and 10B are graphs comparing the axial and lateraldisplacements, respectively, of a standard conical tip and thedual-taper tip of FIG. 9A subject to axial and radial loads;

FIG. 11 is a schematic elevational view of a catheter tip of the presentinvention having various lengths for increased flexibility;

FIGS. 12A–12C are Finite Element models of three catheter tips of thepresent invention, all being subjected to the same lateral load;

FIG. 13A is a longitudinal sectional view through a catheter distal tipof the present invention;

FIGS. 13B and 13C are transverse sectional views through the catheter ofFIG. 13A, taken along lines 13B—13B and 13C—13C, respectively,illustrating the different cross-sectional areas of primary and medicalimplement lumens at those two locations; and

FIG. 14A is perspective view of an alternative catheter distal tip ofthe present invention made of two materials.

FIG. 14B is a perspective view of another alternative catheter distaltip of the present invention, that facilitates attachment of opticalfibers in a medical implement lumen at a distal end of the catheter tip.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description, and the figures to which it refers,are provided for the purpose of describing example(s) and specificembodiment(s) of the invention only and are not intended to exhaustivelydescribe all possible examples and embodiments of the invention.

The present invention primarily relates to an improved central venouscatheter having at least one optical fiber, and preferably a plurality,for measuring oxygen saturation of venous blood. Indeed, though theexamples used herein are central venous catheters, it should beunderstood that various aspects of the invention are generic to anycatheter used in the body that requires a soft distal tip. That includescatheters that are inserted over a guidewire using the Seldingertechnique, and other soft-tipped catheters that are inserted using othermeans. In particular, the various constructions of the soft tip of thecatheters described herein may be applied to other than central venouscatheters. This is not to say that all catheters can be interchanged andused for all purposes. For example, catheters that are inserted usingthe Seldinger technique must have a tapered tip.

Furthermore, various exemplary embodiments of the present inventionmaintain the soft, flexible nature of the distal tip of the catheterwhile also utilizing somewhat stiffer optical fibers therethrough.However, the invention is not limited to optical fibers, and any medicalimplement passed through the catheter to its distal tip may besubstituted.

Prior to a discussion of the various advantageous aspects of the novelcatheters of the present invention, various prior art catheters will bedescribed.

FIGS. 1A and 1B schematically illustrate the distal end of a prior artcentral venous catheter 20. As mentioned above, central venous cathetersare introduced into the venous system using the Seldinger technique,which involves advancing the catheter 20 over a previously insertedguidewire. This will be more clearly described with respect to FIGS. 2and 3, but catheter 20 includes a tapered, soft distal tip 22 formed onthe end of, or otherwise attached to, a main catheter body 24. Thelength of the tip 22 is shown as LTIP, which is typically around 6.35 mm(0.25 inches), and no more than 7.4 mm (0.29 inches). FIG. 1B is a viewof the end of the catheter 20 which illustrates that the largest outerdiameter of the tip 22 is as large as the outer diameter of catheterbody 24.

The soft tip 22 is typically constructed separately from the catheterbody 24 and attached thereto using adhesive or heat bonding. Thecatheter body 24 is relatively flexible so as to easily pass throughcourtesy in the venous vasculature. Exemplary materials for the catheterbody 24 include Tecoflex and Pellethane. The soft tip 22 is relativelymore flexible than the body 24, and is typically made of Tecoflex.

The catheter body 24 includes a generally centered through lumen 26 thatis aligned with a generally centered through lumen 28 in the soft tip22. These aligned lumens 26, 28 permit the catheter 22 to ride over theguidewire. Furthermore, once properly inserted, the guidewire can beremoved and fluid can be passed through the lumens 26, 28. The catheterbody 24 further includes a pair of auxiliary lumens 30 a, 30 b that areshown closed at their distal ends. Each of these auxiliary lumens 30 a,30 b communicates with the interior of the body vessel through a sideport 32 a, 32 b located just proximal to the end of the catheter body24. Therefore, fluid may be infused through the lumens 30 a, 30 b andside port 32 a, 32 b into the target vessel. Although not shown, sometype of radiopaque or otherwise imageable marker is typically providedon the tip 22 for the purpose of locating the tip within the body.

It is important to note that the central venous catheter 20 has only asingle lumen (aligned lumens 26, 28) that extends to the soft tip 22which is used for passing a guidewire during insertion, and later forfluid infusion. Such a lumen extending through the distal tip 22 cannothave any medical implement, for example, a sensor or a probe, locatedwithin it because such an implement would compromise the flexibility ofthe soft tip and would also interfere with the passing of the guidewireduring insertion.

Now with reference to FIGS. 2–4, the shapes of the distal ends ofvarious catheters are shown in conjunction with their use. FIG. 2A showsa conventional CV catheter 20 having a tapered tip 22, such as thatshown in FIGS. 1A and 1B, riding over a guidewire 40 that has previouslybeen inserted into a body vessel 42. The guidewire 40 passes through aninsertion path 44 formed in the surrounding tissue and the wall ofvessel 42. Typically, this insertion path 44 is first formed with aneedle and a guidewire inserted therethrough. Subsequently, a tubularinstrument known as a dilator is inserted over the guidewire and pushedthrough the tissues surrounding the puncture hole and into the vessel.This creates a large enough opening for the tapered catheter 20. FIG. 2Bis a schematic graph of the force required to push the catheter 20through the insertion path 44. A relatively low insertion force isrequired to pass the catheter 20 into the vessel 42, which is preferredby the operator.

FIG. 3A shows another exemplary catheter 50 of the prior art that has arelatively blunt and rigid tip 52. The catheter 50 is shown riding overa guidewire 54 that has previously been inserted into a body vessel 56through an insertion path 58. Forcing the blunt tip 52 through theinsertion path 58 results in the insertion force graph of FIG. 3B. Thatis, in contrast to the graph of FIG. 2B for the tapered tip 22, theinsertion force required is much larger. Disadvantageously, the higherforces are transmitted to the catheter body which may tend to buckle,and the catheter may cause trauma to the tissue surrounding theinsertion path 58. Furthermore, the operator experiences difficulty ininserting the catheter 50 into the vessel 56, which is disconcerting andmakes the task more difficult.

For comparison, FIG. 4 illustrates a typical prior art pulmonary artery(PA) catheter tip 60 that also includes a blunt or flat end face 62 thatprovides a terminus for the fiber optics therein. Because of this bluntend face 62, insertion using the Seldinger technique, as with thecatheter shown in FIG. 3A, results in high insertion forces andpotential damage to the surrounding tissue. The PA catheter 60 furtherincludes a recessed region 64 near its distal end for mounting anexpansion balloon, which stiffens the distal tip.

Oximetry PA catheters also have a blunt or flat distal tip whichprovides an interface with a calibrating media for the fiber-opticstherein. Specifically, the distal end of the catheter with the fiberoptics is held in contact with an in vitro calibrating device whichpermits calibration of the catheter without drawing a blood sample fromthe patient. Oximetry PA catheters include an expansion balloon on theirdistal end for stiffening the tip. PA catheters with rigid blunt tipsare acceptable in light of their use and insertion techniques, and theyeven have several advantages; they are easily manufactured, polishing ofthe distal end of the fibers is easy, and preparation of the expansionballoon is relatively easy. Further, the rigid tip facilitatespositioning within the in vitro calibration device while maintainingintimate contact with the calibrating media. However, the rigidity ofthe distal tip of such catheters is undesirable in the central venousenvironment.

There is believed to be only one commercially available central venous(CV) catheter with oximetry, available from Edwards Lifesciences ofIrvine Calif. The distal end of this catheter is illustrated in FIGS.5A–5B and 6A–6B, and includes a multi-lumen catheter body 70, a reduceddiameter distal portion 72 for insertion into a calibration device, anda formed distal tip 74. The distal tip includes a flat end face 76providing a terminus for a primary lumen 78 and a smaller fiber-opticlumen 80 housing at least two optical fibers 82. The catheter is formedof a single, homogeneous material and the reduced diameter distalportion 72 is thermo-formed on the end of the extruded catheter body 70.The forming process renders the distal portion 72 and distal tip 74relatively rigid.

With reference to FIG. 5B and FIGS. 6A–6B, the catheter body 70 housesfour lumens; the aforementioned primary lumen 78 and fiber-optic lumen80, as well as a pair of infusion lumens 84 a, 84 b that open throughthe side wall of the catheter body 70 at a pair of side ports 86 a, 86b. The infusion lumens 84 a, 84 b terminate at dead-end walls 88 at thedistal end of the catheter body 70. Therefore, only the primary lumen 78and fiberoptic lumen 80 extend through the entire catheter to the distalend face 76, which also contributes to rendering the distal portion 72stiff because there is a smaller air-to-material ratio.

The CV oximetry catheter shown in FIGS. 5 and 6 is not an ideal design.Although the formed distal tip 74 is tapered, the distal end face 76 isflat to accommodate the fiber optics which results in a fairly rigidblunt tip similar to a PA catheter, such as shown in FIG. 4. The bluntrigid tip is difficult to insert into a vessel using the Seldingertechnique and increases the risk of vessel perforation once in thevessel, compared to a soft tip CV catheter. As mentioned above, apreferred CV catheter has a soft, tapered distal tip.

More generally, there are three basic requirements of a CV catheterdistal tip, with or without the presence of the medical implement.First, the column strength of the catheter tip should be maximizedduring insertion over the guidewire so as to prevent buckling. Secondly,the column strength of the catheter tip once the guidewire is removedshould be minimized. More particularly, the tip should collapse easilyif an axial load is applied, which is particularly important if thecatheter migrates into the right atrium. Finally, the bend resistance ofthe catheter tip should be minimized so the tip will bend if it comes incontact with the vessel wall. Unfortunately, adding fiber optics or anyother medical implement to a catheter distal tip normally undermines thelast two flexibility requirements.

In answer to the problems of prior catheters and to present a solutionmeeting the above three requirements, the present invention provides amultiple lumen CV catheter which has a multiple lumen soft distal tipthat stiff enough to resist buckling during insertion and flexiblethereafter despite the presence of a medical implement in at least oneof the lumens of the catheter that extends through the distal tip of thecatheter.

FIGS. 7A–7C illustrate an exemplary a catheter 80 of the presentinvention which provides these features. The catheter 80 has a catheterbody 88 and a catheter distal tip 82. The catheter tip 82 is taperedfrom a small diameter distal end face 84 outward to a relatively largerdiameter proximal end face 86 that abuts an interface 89 of a catheterbody 88. The catheter tip 82, or at least some portion thereof, has asofter durometer than the material of the body 88, and may be made ofthe same or different material. If made of a different material, thecatheter tip 82 attaches to the distal end of the catheter body 88 atthe interface 89 using, for example, adhesive or other bonding means.Alternatively, the tip 82 and body 88 may be made of the same material,with the tip being more flexible by virtue of a construction of thinnerwalls or a higher air-to-material ratio cross-section then the catheterbody. Suitable materials include, but are not limited to, polyurethane,silicone, or polyvinylchloride (PVC), KRATON, or any medical gradeelastomer.

For purposes of this application, the term “soft tip” (or similar termsused herein) means a catheter tip that meets all three above describedrequirements. As a more specific example, it means that, for instance,at least a bending portion of the tip 82 should have a Shore A hardnessof less than the catheter body 88, and more particularly less than 100.Stated another way, at least a bending portion of the distal tip 82should be sufficiently soft and flexible so as to deform or collapsewhen it encounters the inner wall of the vessel or the heart wall.

The catheter 80 thus has the required properties mentioned above, thatis, its distal tip 82 has sufficient column strength to resist bucklingduring insertion over a guidewire, but is sufficiently flexible todeform when subjected to axial or radial loads in the absence of theguidewire and its bend resistance should be minimized. Again, it shouldbe noted that although the catheter 80 is particularly useful as a CVcatheter with oximetry or other sensors, different catheters, such aspulmonary artery and peripheral axis catheters, could also benefit fromits novel features, as disclosed in copending patent application Ser.No. 10/195,954, entitled “MULTIPLE LUMEN CATHETER HAVING A SOFT TIP,”filed Jul. 16, 2002.

The catheter 80 has multiple lumens, at least one of which is normallyassociated with infusing fluid and withdrawing blood samples, and atleast one other associated with placement or positioning of a biomedicalsensor or other medical implement. In the illustrated embodiment, thecatheter body 88 has a primary lumen 90, a device or medical implementlumen 92, and an auxiliary lumen 94. The catheter tip 82 has a primarylumen 96 and a medical implement lumen 98. Both the primary and medicalimplement lumens 90, 92 in the catheter body 88 align with the primaryand medical implement lumens 96, 98 and extend through the catheter tip82 and open at the distal end face 84. The aligned medical implementlumens 92 and 98 and the aligned primary lumens 90 and 96 could bealternatively described as a single medical implement lumen extendingthrough the catheter body and the catheter tip and as a single primarylumen extending through the catheter body and the catheter tip,respectively. In contrast, the auxiliary fluid lumen 94 terminates atthe distal end of the catheter body 88 and opens at a side port 100.

In the illustrated embodiment, a medical implement is a biomedicalsensor extending through the medical implement lumens 92, 98 whichcomprises, as an example, one or more optical fibers 102 used totransmit and receive light for measuring oxygen saturation. In otherconfigurations within the scope of the present invention, the medicalimplement lumens 92, 98 may be used to pass various other medicalimplements or sensors, for example, temperature sensors, or pressuresensors, or pH sensors, or pacing leads, or pacing electrodes, orprobes. FIGS. 7B–7C illustrate the transverse cross-section of thecatheter tip 82, and it can be seen that the primary lumen 96 intersectsthe central axis of the catheter 80 but is offset in one direction withrespect thereto. The medical implement lumen 98 is shown elongated andarcuate, although other configurations, dimensions, shapes and relativepositions of both lumens 96 and 98 are possible and within the scope ofthe present invention. Moreover, the central venous catheter of thepresent invention may have additional lumens, some of which mayterminate like the lumen 94 at a side port proximally to the distal tipwhile others may also extend through the catheter distal tip 82.Furthermore, the catheter body 88 of the present invention may have onlya medical implement lumen 92 and a primary lumen 90 (aligned with thecorresponding medical implement lumen 98 and the primary lumen 96 of thedistal tip), without an auxiliary lumen 94.

The optical fibers 102 (or other above-mentioned medical implements) aredesirably fastened or secured within the distal tip 82 so as to preventtheir migration. Another aspect of the present invention is that thefibers 102 are secured in a manner that does not compromise theflexibility and other required features of the soft tip 82. For example,the medical implement lumen 98 is shown tapering down from a proximalend of the catheter tip (which is the area adjacent to and incorporatingthe proximal end face 86) toward the distal end of the catheter tip(which is the area adjacent to and incorporating the distal end face84). A short portion 104 of the medical implement lumen 98 at a distalend of the catheter tip extending proximally from the distal end face 84does not need to taper, but is rather sized just larger than thediameter of the fibers 102. Only in this portion 104 are the fibers 102secured to the catheter tip 82, for example, by adhesive. Because theportion 104 is limited in axial length, the length along which adhesiveor other means for attachment is provided is also limited. Preferably,the portion 104 extends axially along a length which is less than 3.5mm, more preferably between 0.5–3.5 mm, and most preferably between 1–2mm.

Typical adhesives used in this context are relatively stiff when cured,and other methods of securement contemplated, such as solvent bonding,heat forming, or ultrasonic bonding, also result in a stiff sectionwhere applied. Even a simple compression fit results in a stiff portionwhere the tip 82 and fibers 102 are in interfering contact.Consequently, the combination of the joined optical fibers 102, adhesive(or other joining technique) applied in prior art along all or asubstantial length of the distal tip 82, and material of the distal tip82 was significantly stiffer and did not fulfill the goals of thecatheter of the present invention. Further, if not managed, bending ofthe region in which the adhesive was applied could cause the adhesive tocrack or otherwise loosen. With the catheter of the present invention,however, because the optical fibers 102 are only secured in this shortportion 104 of the medical implement lumen 98, the remainder of theouter fibers remain free to slide with respect to the medical implementlumens 92 or 98. Therefore, when an axial or radial load is imparted todistal tip 82, the tip deforms or buckles in the region that is proximalto this short portion 104. The very distal end of the tip 82 isrelatively stiffer, but this does not compromise the performancecharacteristics of the catheter as mentioned above.

FIG. 8A is a perspective view of an alternative soft multiple lumencatheter tip 110 on the end of the catheter body 112 of the presentinvention that does not have a sensor fixed therein, such as the fiberoptics 102 disclosed above. Instead, the soft distal tip 110 includes aprimary lumen 114 and a medical implement lumen 116 that receivessensors. FIG. 8B is a longitudinal sectional view of the soft distal tip110 and catheter body 112 that are either secured together at aninterface 118, or formed of a homogeneous material. The primary lumen114 and the medical implement lumen 116 are aligned with orcontinuations of similar lumens in the catheter body 112 as shown. Apair of auxiliary lumens 120 a, 120 b that each opens at side ports 122a, 122 b may be provided in the catheter body 112. FIG. 8B also shows anelongated probe 130 that has a connector 132 at its proximal end and asensor 134 at its distal end. The probe 130 is sized to pass through themedical implement lumen 116 and may be utilized at or near the distalface 124 of the catheter tip 110. Sensors that can be used includefiber-optics, temperature sensors, pH sensors, pressure sensors, asensor for cardiac pacing, and the like. Once again, because the distaltip 110 is soft (i.e., softer than catheter body 112), and because theprobe 130 is not secured within the medical implement lumen 116, thesoft distal tip easily deforms upon application of axial or radialforces.

As mentioned above, the various distal tips of the catheters of thepresent invention are made softer than the main catheter body, andpreferably soft enough to easily deform upon contact with thesurrounding vessel wall or heart wall. To do this, the distal tips aremade of a soft material and/or are constructed in a way that they flexeasily.

For example, FIGS. 9A–9E illustrate a soft catheter tip 140 that has atapered proximal region 142 and distal region 144 that has a narrowertaper, the two regions meeting at an elbow 146. FIG. 9D is a sectionthrough the proximal region 142, and FIG. 9E is a section through thedistal region 144. The length of the proximal region 142 is shown as L₁,while the length of distal region 144 is shown as L₂. The total lengthof the distal tip 140 is given as L_(TIP). In an exemplary embodiment,L_(TIP) is about 7.6 mm (0.30 inches), and L₁ and L₂ are approximatelyequal. Alternatively, L₁ and L₂ may be unequal with the longer of thetwo lengths being preferably more flexible than the other. The exemplarytaper angle of the proximal region 142 is about 30°, while the exemplarytaper angle of the distal region 144 is about 15°. Other angles of taperare also within the scope of the present invention.

FIG. 9C is a schematic view of the distal tip showing in phantom theline 150 of a tip having a single taper. The cross-hatched region 152 isthe volume of material that is removed to result in the differing tapersof the proximal region 142 and distal region 144. The reduction of theoverall material in the center of the tip allows for a bending focalpoint.

FIGS. 9D and 9E illustrate the respective air-to-material ratios in theproximal region 142 and the distal region 144. As seen, there is agreater volume of air to material in the proximal region 142 than in thedistal region 144. Therefore, the bending stiffness of the proximalregion is less than that of the distal region. As a result, axial orradial forces imparted to the distal end face 154 of the tip 140 willcause bending in the proximal region 142 rather than in the distalregion 144. Because of this, sensors placed through, or fixed in amedical implement lumen 156, are positioned within a relatively stiffdistal region which is beneficial in some instances, such as whencalibrating fiber optics.

Alternatively, rather than removing material from the exterior of thedistal tip 140, the lumens 156 and 158 may be enlarged within the tip toresult in the same effect. That is, more material may be removed toenlarge the lumens in the proximal portion 142 to create a largerair-to-material ratio therein. This is shown further in FIGS. 13A–13C.Of course, various combinations of the two can also be utilized.

FIGS. 10A and 10B are graphs that illustrate the column strength andflexural strength, respectively, of the standard conical tip and adual-tapered tip, such as that shown in FIG. 9A. In both graphs, theapplied force in pounds is indicated at the left along the verticalaxis, while the corresponding displacement of the respective tips ininches is shown along the horizontal axis. As indicated, thedual-tapered tip displaces farther in either case at lower appliedforces. This means that the dual-tapered tip more easily buckles upon anapplied axial force and bends more easily upon an applied radial force.

FIG. 11 schematically illustrates several superimposed soft catheterdistal tips 160 a, 160 b, 160 c having gradually longer lengths L₁, L₂,L₃, respectively. Each of these tips 160 has a single conical taper andis otherwise cylindrical and configured much like previously describedcatheter distal tips. A radial force F is shown applied near the distalend of each of the tabs. One way to render the tip more flexible is toincrease its length. Therefore, the longest tip 160 c will bend thefarthest distance from the implied force F because of the longer leverarm. For multiple lumen soft catheter tips of the present invention, thelength should be at least 5.1 mm (0.20 inches), and preferably at leastabout 7.6 mm (0.30 inches). An additional benefit of increasing thelength of the distal tip is that the taper angle is reduced, whichreduces the resistance to insertion using the Seldinger technique, andconsequently reduces the required column strength of the distal tip.

FIGS. 12A–12C are Finite Element models of different catheter tips ofthe present invention, each under the same radial or lateral load. FIG.12A shows a deflected tip 170 that is made of a single homogeneousmaterial, and the corresponding relaxed state is seen in phantom. FIG.12B shows a tip 172 that has a proximal region 174 made of the samematerial as the entire tip 170 in FIG. 12A, and a distal region 176 madeof a softer material (i.e., more flexible). Accordingly, the distalregion 176 curls and deflects more than the distal portion of tip 170 inFIG. 12A. Finally, FIG. 12C illustrates a tip 180 that has a distalregion 182 made of the same material as the entire tip 170 in FIG. 12A,and a proximal region 184 made of a softer material (i.e., moreflexible). Therefore, under load, the tip 180 bends more than tip 170 inFIG. 12A. The behavior of tip 180 under a lateral load approximates thatof the tips discussed above that have optical fibers glued to theirdistal ends, thus making the distal region more stiff than the proximalregion. The lengths of the regions may be equal or not, and the tips maybe made from the various material discussed herein, such as Pellethaneand Tecothane, both urethanes. The softer of the two materials, or inother words the bending portion, preferably has a durometer of less than100 Shore A, more particularly between about 45–100 Shore A, mostdesirably about 75 Shore A.

FIGS. 13A–13C illustrate a further configuration for rendering a portionof the catheter distal tip more soft and flexible than the rest of thecatheter body. Specifically, FIG. 13A shows the distal tip 190 having aproximal region shown in cross-section in FIG. 13B and a distal regionshown in cross-section in FIG. 13C. As can be seen, a medical implementlumen 192 and a primary lumen 194 are reduced in size in the distalregion shown in FIG. 13C. This means that the air-to-material ratio inthe distal region is less than that in the proximal region, and thus thedistal tip 190 bends or buckles in the proximal region. Anotheralternative embodiment of the present invention may combine a dual-tapertip of the catheter with the different materials of various portions ofthe distal tip. One exemplary configuration of the dual-material,dual-taper is where the proximal segment consists of a high durometermaterial while the distal segment consists of a lower durometermaterial. This configuration creates a very flexible tip with low columnstrength.

A further example of a soft-tipped catheter of the present invention isseen in FIG. 14A. In this aspect of the present invention, a catheterbody 200 attaches at an interface 202 to a distal tip 204 formed of twomaterials. A proximal region 206 of the catheter tip 204 is formed of afirst material and a distal region 208 of the catheter tip is formed ofa second material. In this embodiment, the catheter tip includes aprimary lumen 210 and a medical implement lumen 212. By way of exampleand not limitation, a medical implement, such as a pair of opticalfibers 214, extend through the medical implement lumen 212. As beforewith reference to FIG. 7, the fibers could be secured by adhesive andthe adhesive could be applied only along a short portion adjacent thedistal face 216, and preferably along a portion between 0.5–3.5 mm inlength.

The two materials of the proximal and distal regions 206, 208 may bemore or less relatively flexible depending on the catheter tip design.For example, if a sensor such as fiber optics is secured in the distalend of the tip, the proximal region is desirably more flexible (softer)so that it provides a point of bending. Various combinations ofmaterials such as polyurethane, silicone, or polyvinylchloride (PVC),KRATON, or any medical grade elastomer may be used to create a cathetertip that is either more flexible in the proximal region or more flexiblein the distal region. Furthermore, various constructional differencesmay accentuate the difference in flexibility.

FIG. 14B illustrates a still further alternative configuration of acatheter distal tip of the present invention. As in FIG. 14A, a catheterbody 220 attaches at an interface 222 to a distal tip 224 formed of twomaterials. In this embodiment, however, a first material 226 forms aproximal region and two generally axially-oriented segments 228 a, 228 bthereof extend on diametrically opposed sides of the distal tip all theway to a distal face 230. Of course, more than two generally axiallyoriented segments, similar to 228 a and 228 b, are within the scope ofthe present invention. A second material 232, which could betransparent, fills the remainder of the spaces between two or moresegments 228 a, 228 b. Optical fibers 234 extend through a medicalimplement lumen 236 and are secured therein with adhesive. As before,the adhesive is only applied along a short portion adjacent the distalface 230, and preferably along a portion between 0.5–3.5 mm in length.

The second material 232 may be transparent or only partly opaque suchthat ultraviolet light can pass therethrough. A suitable adhesive is onethat is cured with ultraviolet light, and the first material 226 isdesirably opaque to prevent such light passing through. In this manner,adhesive can be injected into the medical implement lumen 236, and uponapplication of ultraviolet light, only a portion that is exposed by thefirst material 226 becomes cured. This reduces the importance of thevolume of adhesive injected into medical implement lumen 236, and thusfacilitates assembly and ensures consistency.

The transparent material 232 in the distal tip provides a window throughwhich ultraviolet light can pass and cure adhesive previously injectedinto the medical implement lumen 236. The first material 226 may beradiopaque such that the side segments 228 a, 228 b provide axiallyoriented markers to guide positioning of the distal tip 224 within thebody.

In assembling the catheter tips of FIGS. 14A and 14B, the dual-materialdistal tips and catheter body may be constructed using an RF tip formingprocess, but techniques such as heat forming or steam forming may alsowork. This involves the use of three extruded tubes, one for thecatheter body, and two others for the dual-material tip. Two mandrelsare inserted through the three tubes and RF tip formed simultaneously.Once the catheter is constructed, the adhesive is drawn into the medicalimplement lumen using a vacuum pump. If the transparent materials areused in the tips, they would provide an advantage in that the depth ofthe adhesive can be visualized. Another alternative is to do without thetransparent material but instead use an opaque or semi-opaque materialthat still permits some ultraviolet light through, and which may beentirely radiopaque. An adhesive that can be cured by ultraviolet lightor heat could be used. Some ultraviolet passes through the tip materialand partially cures the adhesive, and the remainder of the curingprocess is done using heat.

The present invention also teaches a method of measuring oxygensaturation of the venous system. The steps of the method are as follows:

-   -   providing a central venous catheter having a catheter body and a        soft, multiple lumen catheter tip, the catheter tip tapering        down from a proximal end to a distal end;    -   providing at least one optical fiber extending through the        catheter body to the distal end of the catheter tip;    -   inserting the central venous catheter into a venous system        vessel using the Seldinger technique;    -   advancing the catheter tip of the central venous catheter into a        location in the venous system for measuring oxygen saturation of        the venous blood; and    -   measuring oxygen saturation of venous blood using the optical        fiber.

The catheter body may include at least one auxiliary fluid infusionlumen and a side port opening adjacent the distal tip, wherein themethod includes infusing fluids through the auxiliary fluid infusionlumen. The distal tip of the catheter preferably comprises a materialthat has a durometer of less than or equal to 100 Shore A hardness.Furthermore, the distal tip of the catheter preferably has a proximalregion and a distal region, and wherein the proximal region has a largertaper angle than the distal region to facilitate insertion using theSeldinger technique.

It will be appreciated that the invention has been described above withreference to certain examples or preferred embodiments as shown in thedrawings. Various additions, deletions, changes and alterations may bemade to the above-described embodiments and examples without departingfrom the intended spirit and scope of this invention. Accordingly, it isintended that all such additions, deletions, changes and alterations beincluded within the scope of the following claims.

1. A multiple lumen central venous catheter having a soft tip,comprising: a generally tubular catheter body having a proximal end anda distal end, the catheter body defining therein at least one primarylumen and at least one medical implement lumen; a soft, tapered distalcatheter tip having a distal end and a proximal end abutting the distalend of the catheter body, the catheter tip defining therein at least oneprimary lumen aligned with the at least one primary lumen of thecatheter body and at least one medical implement lumen aligned with theat least one medical implement lumen of the catheter body, wherein thecatheter tip has a proximal region and a distal region, and wherein theproximal region is more flexible than the distal region and moreflexible than the catheter body and forms a bending portion of thecatheter tip; and at least one optical fiber extending through the atleast one medical implement lumen of the catheter body and the at leastone medical implement lumen of the catheter tip, and being securedthereto only at the distal end of the catheter tip.
 2. The centralvenous catheter of claim 1, wherein the at least one optical fiberextends to a distal face of the catheter tip and is secured thereto. 3.The central venous catheter of claim 1, wherein the optical fiber issecured using adhesive that is only applied along a short portion of themedical implement lumen of the catheter tip having an axial length ofbetween 0.5–3.5 mm.
 4. The central venous catheter of claim 3, whereinthe adhesive is cured by ultraviolet light, and wherein a portion of thecatheter tip permits passage of ultraviolet light therethrough into themedical implement lumen.
 5. The central venous catheter of claim 4,wherein the catheter tip is formed of two materials, one materialcomprising the portion that permits passage of ultraviolet light, andanother material that provides a radiopaque marker.
 6. The centralvenous catheter of claim 1, wherein the catheter tip is tapered to havea smaller diameter on its distal end than on its proximal end and has aproximal region and a distal region, the catheter tip having at leasttwo exterior taper angles, and wherein the proximal region has a greatertaper angle than the distal region.
 7. The central venous catheter ofclaim 1, wherein the proximal region is made of a material that has adurometer of less than or equal to 100 Shore A hardness.
 8. The centralvenous catheter of claim 1, wherein the proximal region has a largerair-to-material ratio in transverse cross-section than the distalregion.
 9. The central venous catheter of claim 8, wherein, intransverse cross-section, both the at least one primary lumen and the atleast one medical implement lumen are enlarged in the proximal regionrelative to the surrounding material in comparison to the relative sizeof the lumens and material in the distal region, such that the proximalregion has a larger air-to-material ratio than the distal region. 10.The central venous catheter of claim 1, wherein the catheter tip has alength of at least 7.6 mm (0.30 inches).
 11. A multiple lumen centralvenous catheter having a soft tip, comprising: a generally tubularcatheter body having a proximal end and a distal end, the catheter bodydefining therein at least one primary lumen and at least one medicalimplement lumen; a soft, tapered distal catheter tip having a distal endand a proximal end abutting the distal end of the catheter body, thecatheter tip defining at least one primary lumen aligned with the atleast one primary lumen of the catheter body and at least one medicalimplement lumen aligned with the at least one medical implement lumen ofthe catheter body, wherein the catheter tip has a proximal region and adistal region and wherein the proximal region is more flexible than thedistal region and is more flexible than the catheter body, and whereinthe proximal region has a larger air-to-material ratio in transversecross-section than the distal region.
 12. The central venous catheter ofclaim 11, wherein the catheter tip is tapered to have a smaller diameteron its distal end than on its proximal end and has at least two exteriortaper angles, and wherein the proximal region has a greater taper anglethan the distal region.
 13. The central venous catheter of claim 11,wherein at least one of the proximal and distal regions is made of amaterial that has a durometer of less than or equal to 100 Shore Ahardness.
 14. The central venous catheter of claim 11, wherein, intransverse cross-section, both the primary lumen and the medicalimplement lumen are enlarged in the proximal region relative to thesurrounding material in comparison to the relative size of the lumensand material in the distal region, such that the proximal region has alarger air-to-material ratio than the distal region.
 15. The centralvenous catheter of claim 11, wherein the catheter tip is formed of twomaterials.
 16. The central venous catheter of claim 11, furthercomprising a medical implement extending through the medical implementlumen of the catheter body and the medical implement lumen of thecatheter tip.
 17. The central venous catheter of claim 16, wherein themedical implement is a sensor for measuring physiologic parametersecured to the medical implement lumen only at the distal end of thecatheter tip.
 18. A multiple lumen central venous catheter having a softtip, comprising: generally tubular catheter body having a proximal endand a distal end, the catheter body defining therein at least oneprimary lumen and at least one medical implement lumen; a soft, tapereddistal catheter tip having a distal end and a proximal end abutting thedistal end of the catheter body, the catheter tip defining at least oneprimary lumen aligned with the at least one primary lumen of thecatheter body and at least one medical implement lumen aligned with theat least one medical implement lumen of the catheter body, wherein thecatheter tip has a proximal region and a distal region, and wherein theproximal region has a larger air-to-material ratio in transversecross-section than the distal region, wherein the catheter tip hassufficient column strength to resist buckling during insertion using theSeldinger technique over a guidewire, but is sufficiently flexible todeform when the tip is subjected to axial or radial loads in the body inthe absence of the guidewire; and a sensor extending through the atleast one medical implement lumen of the catheter body and the at leastone medical implement lumen of the catheter tip.
 19. The central venouscatheter of claim 18, wherein the sensor is secured only at the distalend of the catheter tip.
 20. The central venous catheter of claim 19,wherein the sensor is secured using adhesive and adhesive is onlyapplied along a short portion of the medical implement lumen having anaxial length of between 0.5–3.5 mm.
 21. The central venous catheter ofclaim 20, wherein the adhesive is cured by ultraviolet light, andwherein a portion of the catheter tip permits passage of ultravioletlight therethrough into the medical implement lumen.
 22. The centralvenous catheter of claim 18, wherein the catheter tip is formed of twomaterials.
 23. The central venous catheter of claim 18, wherein thesensor is selected from the group consisting of: one or more opticalfibers; a pH sensor; a pressure sensor; a temperature sensor; at leastone pacing lead; a pacing probe; and a pacing electrode.
 24. The centralvenous catheter of claim 18, wherein the catheter tip has a proximalregion and a distal region, and wherein the distal region has adifferent durometer than the proximal region.
 25. The central venouscatheter of claim 18, wherein the catheter tip has a proximal region anda distal region, and wherein at least one of the proximal and distalregions is made of a material that has a durometer of less than or equalto 100 Shore A hardness.
 26. The central venous catheter of claim 18,wherein the catheter tip has a proximal region and a distal region, andwherein one of the proximal region and the distal region is moreflexible than the other region.
 27. The central venous catheter of claim18, wherein the catheter tip is tapered to have a smaller diameter onits distal end than on its proximal end and has a proximal region and adistal region, and at least two exterior tapered angles, and wherein theproximal region has a greater taper angle than the distal region. 28.The central venous catheter of claim 18, wherein the sensor is a probethat fits through the medical implement lumens and is removable from thecatheter.
 29. A multiple lumen central venous catheter having a softtip, comprising: a generally tubular catheter body having a proximal endand a distal end, the catheter body defining therein at least oneprimary lumen and at least one medical implement lumen; a soft, tapereddistal catheter tip having a distal end and a proximal end abutting thedistal end of the catheter body, the catheter tip defining at least oneprimary lumen aligned with the at least one primary lumen of thecatheter body and at least one medical implement lumen aligned with theat least one medical implement lumen of the catheter body, wherein thecatheter tip has sufficient column strength to resist buckling duringinsertion using the Seldinger technique over a guidewire, but issufficiently flexible to deform when the tip is subjected to axial orradial loads in the body in the absence of the guidewire; and a sensorextending through the at least one medical implement lumen of thecatheter body and the at least one medical implement lumen of tocatheter tip and secured only at the distal end of the catheter tip. 30.The central venous catheter of claim 29, wherein the sensor is securedusing adhesive and adhesive is only applied along a short portion of themedical implement lumen having an axial length of between 0.5–3.5 mm.31. The central venous catheter of claim 30, wherein the adhesive iscured by ultraviolet light, and wherein a portion of the catheter tippermits passage of ultraviolet light therethrough into to medicalimplement lumen.
 32. The central venous catheter of claim 29, whereinthe catheter tip is formed of two materials.
 33. The central venouscatheter of claim 29, wherein the catheter tip has a proximal region anda distal region, and wherein the distal region has a different durometerthan the proximal region.
 34. The central venous catheter of claim 29,wherein the catheter tip has a proximal region and a distal region, andwherein at least one of the proximal and distal regions is made of amaterial that has a durometer of less than or equal to 100 Shore Ahardness.
 35. The central venous catheter of claim 29, wherein thecatheter tip has a proximal region and a distal region, and wherein oneof the proximal region and the distal region is more flexible than theother region.
 36. The central venous catheter of claim 29, wherein thecatheter tip is tapered to have a smaller diameter on its distal endthan on its proximal end and has a proximal region and a distal region,and at least two exterior tapered angles, and wherein the proximalregion has a greater taper angle than the distal region.
 37. The centralvenous catheter of claim 29, wherein the sensor comprises one or moreoptical fibers.
 38. The central venous catheter of claim 29, wherein thesensor is selected from the group consisting of: a pH sensor; a pressuresensor; a temperature sensor; at least one pacing lead; a pacing probe;and a pacing electrode.
 39. A multiple lumen central venous catheterhaving a soft tip, comprising: a generally tubular catheter body havinga proximal end and a distal end, the catheter body defining therein atleast one primary lumen and at least one medical implement lumen; a softtapered distal catheter tip having a distal end and a proximal endabutting the distal end of the catheter body, the catheter tip definingtherein at least one primary lumen aligned with the at least one primarylumen of the catheter body and at least one medical implement lumenaligned with the at least one medical implement lumen of the catheterbody; and at least one optical fiber extending through the at least onemedical implement lumen of the catheter body and the at least onemedical implement lumen of the catheter tip, and being secured theretoonly at the distal end of the catheter tip, wherein the optical fiber issecured using adhesive that is only applied along a short portion of themedical implement lumen of the catheter tip having an axial length ofbetween 0.5–3.5 mm, wherein the adhesive is cured by ultraviolet light,and wherein the catheter tip is formed of two materials, one materialcomprising a portion of the catheter tip that permits passage ofultraviolet light therethrough into the medical implement lumen, andanother material that provides a radiopaque marker.